1. Field of the Invention
The present invention relates to microlithography, and more particularly, to illumination systems for microlithographic equipment that have high numerical apertures.
2. Related Art
Photolithography (also called microlithography) is used for manufacturing of semiconductor devices. Photolithography uses electromagnetic radiation, such as ultraviolet (UV), deep UV or visible light to generate fine patterns in a semiconductor device design. Many types of semiconductor devices, such as diodes, transistors, and integrated circuits, can be fabricated using photolithographic techniques. Exposure systems or tools are used to implement photolithographic techniques, such as etching, in semiconductor fabrication. An exposure system typically includes an illumination system, a reticle (also called a mask) containing a circuit pattern, a projection-system, and a wafer alignment stage for aligning a photosensitive resist-covered semiconductor wafer. The illumination system illuminates a region of the reticle with a preferably rectangular slot illumination field. The projection system projects an image of the illuminated region of the reticle circuit pattern onto the wafer.
As semiconductor device manufacturing technology advances, there are ever increasing demands on each component of the photolithography system used to manufacture the semiconductor device. This includes the illumination system used to illuminate the reticle. For example, there is a need to illuminate the reticle with an illumination field having uniform irradiance. In step-and-scan photolithography, there is also a need to vary a size of the illumination field so that the size of the illumination field can be tailored to different applications and semiconductor die dimensions.
Some illumination systems include an array or diffractive scattering optical element positioned before the reticle. The scattering optical element produces a desired angular light distribution that is subsequently imaged or relayed to the reticle.
Additionally, commonly-used die dimensions are 26xc3x975 mm, 17xc3x975 mm, and 11xc3x975 mm. Thus, a standard zoom lens needs to accommodate variation in the size of the illumination field. However, a particular problem arises in the field of microlithography, where different features that are required to be formed on the semiconductor substrate require variable partial coherence on the part of the exposure optics. Specifically, partial coherence ("sgr"), which in microlithography is commonly defined as the ratio of a numerical aperture of the illumination optics and a numerical aperture of the projection system, needs to vary depending on the nature of the feature being formed on the semiconductor substrate, e.g., the "sgr" for trench formation may be different from the "sgr" for line formation.
Accordingly, a need exists for a simple microlithographic system that can vary the partial coherence parameter over a large range, while simultaneously being able to accommodate different field sizes.
The present invention is directed to a microlithographic system that has variable partial coherence and field size.
One advantage of the present invention is being able to provide a microlithographic system with continuously adjustable partial coherence and discretely adjustable field size.
Another advantage of the present invention is being able to provide a microlithographic system where both partial coherence and field size can vary continuously.
Another advantage of the present invention is being able to provide a microlithographic system that can achieve the above objectives with the use of simple optics.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a system for microlithography comprising an illumination source; an illumination optical system including, in order from an objective side, (a) a first diffractive optical element that receives illumination from the illumination source, (b) a zoom lens, (c) a second diffractive optical element, (d) a condenser lens, (e) a relay lens, and (f) a reticle, and a projection optical system for imaging the reticle onto a substrate, wherein the system for microlithography provides a zoomable numerical aperture.
In another aspect of the present invention there is provided a system for microlithography comprising an illumination source, an illumination optical system that receives illumination from the illumination source, and a projection optical system that receives illumination from the illumination system, wherein a ratio of a numerical aperture of the illumination system and a numerical aperture of the projection optical system is continuously variable while a field size is discretely variable.
In another aspect of the present invention there is provided an illumination system for microlithography comprising, in order from an objective side a first diffractive optical element, a zoom lens, a second diffractive optical element having a rectangular numerical aperture, a condenser lens, and a relay lens.
In another aspect of the present invention there is provided a system for microlithography comprising an illumination system including, in order from an objective side, (a) a zoom lens having a first diffractive optical element on a first side, and a second diffractive optical element on a second side, (b) a condenser lens, and (c) a relay lens, and a projection optical system, wherein a ratio of a numerical aperture of the illumination system and a numerical aperture of the projection optical system is continuously variable.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.